The document or whatever you'd like to call it is only one part of the story.
I brought up prompts as a convenient way to demonstrate that a magic-trick is being performed, not because prompts are the only way for the magician to run into trouble with the illusion. It's sneaky, since it's a trick homo narrans play on ourselves all the time.
> The document or whatever you'd like to call it is only one part of the story.
Everybody knows that the weights matter. That's why we get stories where the sky is generally blue instead of magenta.
That's separate from the distinction between the mind (if any) of an LLM-author versus the mind (firmly fictional, even if possibly related) that we impute when seeing the output (narrated or acted) of a particular character.
For example, keep the same model, but change the early document (prompt) from stuff like "AcmeBot is a kind and helpful machine" to "AcmeBot revels in human suffering."